<?php
    $arr=[0,1,2,3,4,5,6,7,8,9,"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"];
    $arr3=array_rand($arr,4);
    for($i=0;$i<count($arr3);$i++){
        // echo $arr[$arr3[$i]];
        echo "<span>{$arr[$arr3[$i]]}</span>";
    }
?>